Invariant HVC size in female canaries singing under testosterone: Unlocking function through neural differentiation,...

Area of Science:

• Neuroscience
• Behavioral Endocrinology
• Avian Biology

Background:

• The song control nucleus HVC (high vocal center) in canaries is a key area for vocal learning and production.
• HVC is thought to enlarge significantly when transitioning from a non-singing to a singing state, driven by testosterone.
• Understanding the neural basis of behavioral plasticity is crucial for vertebrate neuroscience.

Purpose of the Study:

• To investigate the structural and molecular changes in the HVC of adult female canaries following testosterone administration.
• To determine if HVC size changes during testosterone-induced song development or if other mechanisms are involved.
• To elucidate the role of gene expression in mediating behavioral plasticity in the adult brain.

Main Methods:

• Utilizing 2-photon in vivo imaging to track neuronal distribution and properties in the HVC over several weeks.
• Administering testosterone to adult female canaries to induce singing behavior.
• Employing spatial transcriptomics to analyze gene expression patterns across the HVC.

Main Results:

• Testosterone administration induced singing behavior in female canaries.
• Despite observed ultrastructural changes in HVC neurons, neuronal spacing and overall HVC size remained unaltered.
• Spatial transcriptomics revealed testosterone-modulated gene networks throughout the HVC, aligning regional transcriptomic profiles in singing birds.
• These molecular changes mimicked the histological appearance of an enlarged HVC without actual size increase.

Conclusions:

• HVC size changes in adult songbirds reflect neuronal phenotypic alterations within a stable anatomical framework, not structural enlargement.
• The non-singing state does not involve reduced brain area volume, preserving the HVC's capacity for lifelong functional differentiation.
• This study provides novel insights into the neural mechanisms underlying behavioral plasticity and gene regulation in the adult vertebrate brain.